Hamilton fastest in second practice, Rosberg 2nd
Lotus' Maldonado and Grosjean spin
Hamilton fastest in first practice, Rosberg 2nd
Marussia & Caterham not in Austin
Bianchi still 'critical but stable'
Image source, Getty ImagesA look at the timesheets from both practice sessions would suggest Lewis Hamilton has had a great day. And until the last 18 minutes of FP2 he had. But then the mechanical gremlins came calling.
How much of an impact will it have on the rest of his weekend? Join me tomorrow from 14:30 BST tomorrow to find out. Until then, it's goodnight and Happy Halloween from me.
Joanna Harran: Would love Fernando to have a decent race result to end the season. Has pushed that car all year, deserves at least a podium.
Mercedes' Lewis Hamilton tells BBC F1 pit lane reporter Jennie Gow that it was not a gearbox issue - it's a fuel leak problem but the team still need to do more investigating.
That's all the track action for today. We'll have all the latest news from the Austin paddock on the F1 pages or via @bbcf1.
There'll be video highlights of that second session, too, along with the best driver interviews. You'll be spoilt for choice.
Final practice starts at 15:00 GMT with qualifying following at 18:00.
Image source, Getty Images1) Hamilton 2) Rosberg 3) Alonso 4) Ricciardo 5) Massa 6) Raikkonen
7) Kvyat 8) Magnussen 9) Button 10) Hulkenberg 11) Bottas 12) Grosjean
13) Vergne 14) Perez 15) Maldonado 16) Sutil 17) Gutierrez 18) Vettel
The cars are just cruising around the track as part of the "virtual safety car" test as mentioned earlier. You can read more about it here.
That's the 14th time in 17 races this season that Lewis Hamilton has finished on top of the pile in second practice. Unfortunately, the shine was taken off the achievement as he missed the final 18 minutes of the session, and vital long-run time, with an as-yet-unidentified unidentified car problem.
Image source, Getty ImagesLewis Hamilton finishes fastest in second practice for the United States Grand Prix.
Sebastian Vettel has managed to get out for the final few minutes and has now upped his lap count to 16. That's still well down on Valtteri Bottas, Kevin Magnussen and Pastor Maldonado who have all done 35.
Jenson Button has finished this session in the top nine at every race this season. That run looks set to continue as the McLaren driver, who has yet to sign a contract for next season, is currently ninth, a few thousandths behind team-mate Kevin Magnussen in eighth.
Everyone is out on track apart from Lewis Hamilton, Nico Hulkenberg and Sebastian Vettel. Nico Rosberg is a ticking along nicely on his long run - it's certainly the German who has had the better fortune of the two Mercedes title rivals today.
Image source, EPALewis Hamilton is out of the car and his car is up on the stands. Will the Mercedes driver get out again in this session? Just 18 minutes remaining and for every second he's in the garage, the Briton is losing valuable long run data gathering time.
Ben Weaver: Will Sunday's race be a repeat of Bahrain? I hope not. My heart won't be up to it!!
Image source, Getty ImagesOh dear. Lewis Hamilton is called into the pits. "We've got an issue with the car," comes the ominous message.
BBC Radio 5 live's Jennie Gow:, external Is this Hamilton Hill or Vettel Verge or have you got a better suggestion?
How about Raikkonen Ridge?
Image source, Getty ImagesWhere is Sebastian Vettel? He's in the garage watching this session. The German has only completed 13 laps and has the 18th fastest time.
So there's gearbox concerns for both Mercedes drivers, with just under 25 minutes remaining. Lewis Hamilton and Nico Rosberg have decided to stay out, though, as not to disrupt their long run.
Lewis Hamilon: "Noticed there's a strange shift coming across the finish line. Fourth [gear] to fifth."
It looks like the attention has turned to long runs, in preparation for Sunday's race. That means the standings are unlikely to change, with Lewis Hamilton top, ahead of Nico Rosberg, Fernando Alonso, Daniel Ricciardo and Felipe Massa.